1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus and image forming method, and a program.
2. Description of the Related Art
In recent years, energy conservation in a main body of an electrophotographic copier/printer has been requested, and with this, reduction in power consumption of individual components of a printer engine as an image forming unit has been required. Especially, a fixing unit, which fuses toner transferred onto a print sheet by application of heat thereby fixing the toner on the print sheet, requires a large amount of electric power in a short period of time, so if power consumption of the fixing unit can be reduced, it brings a great effect on energy conservation.
Conventionally, there is known a technology to control fixing temperature according to printing conditions, such as a type of sheet, the thickness of the sheet, and the sheet conveying speed associated with these. However, it is difficult to stabilize the preset temperature of a fixing unit to a target temperature for a certain period of time due to a usage environment and a temporal change of a component, etc.; therefore, in most cases, the preset temperature is set to a rather high temperature to prevent a trouble, such as cold offset, at the time of fixing. Furthermore, in some cases, fixing is performed at the uniform preset temperature regardless of a type of input image (a photo image, a text image, etc.), a type of gradation processing (halftone dot, line screen, dispersed dot, etc.), and the like. Therefore, for example, for a text image in which an area of a gradation processing pattern used in printing and a drawing area are relatively small, the preset temperature is too high, and electric power is consumed more than necessary.
Incidentally, for example, in a technology disclosed in Japanese Patent Application Laid-open No. 2009-14997, in view of the fact that the preset temperature of a fixing unit changes according to a usage environment and due to a temporal change of a component, etc., and this brings a change in image quality of a print image, temperature information of the fixing unit is acquired, and a density-gradation correction parameter is determined on the basis of the temperature information, thereby suppressing a change in image quality of a print image; however, reduction in power consumption is not resolved.